In the past, a blood sample contained in a tube has either been coagulated or else it has been centrifuged. If centrifuged, the red corpuscles which correspond to substantially 60% (by volume) of whole blood separate from the plasma and collect in the bottom of the tube. An operator then uses a pipette disposed above the red corpuscles to take off the quantity of plasma required for the intended analyses. If the operator is clumsy about the separation zone between the two phases, one or other of the following two situations may arise:
a significant amount of plasma to be collected is lost; or
red corpuscles enter the pipette and contaminate the plasma for analysis.
An object of the present invention is to avoid this drawback and to separate plasma automatically from a blood sample without manual intervention and without contamination, and as soon as the sample has been taken, without waiting for coagulation, and to do this at very low cost.